1. Presented to PGDTF February 11, 2015
TPL Standard Status Update
Reliability Standard TPL Transmission System Planned Performance for Geomagnetic Disturbance Events
Presented to PGDTF
February 11, 2015

2. TPL-007-1 Standard Status Update
TPL developed to address FERC Order 779 directives requiring to conduct initial and on-going assessments of the potential impact of benchmark GMD events on the Bulk-Power System, to identify benchmark GMD events that specify what severity GMD events applicable registered entities must assess for potential impacts on the Bulk-Power System and to develop and implement a plan to mitigate the risk of instability, uncontrolled separation, or Cascading as a result of a benchmark GMD event if the assessments identify potential impacts from benchmark GMD events.
A final ballot for TPL concluded December 16, 2014 achieved a quorum and received sufficient affirmative votes for approval.
On January 21, 2015, NERC filed a petition seeking FERC approval of Proposed Reliability Standard TPL-007-1, Transmission System Planned Performance for Geomagnetic Disturbance Events.
Quorum /Approval
84.27% / 78.05%

3. Existing Guidance for Performing GMD Analysis & Modeling Gaps
The NERC GMD TF has developed general guidelines for performing GMD Vulnerability Assessments that are described in TPL :
NERC Geomagnetic Disturbance Planning Guide
NERC GIC Application Guide
Gaps exist in:
GIC modeling
Power flow studies
Harmonics studies
Transformer thermal analysis (to be completed by TO’s and GO’s)

4. Implementation Plan 6 Months 18 Months 24 Months 48 Months 60 Months
Date of Approval
6 Months R1
Identify Responsibilities
18 Months R2
System Models
24 Months R5
GIC Flow Information
48 Months R6
Thermal Assessment
60 Months
R3, R4, and R7
GMD Assessment
Corrective Action Plan

5. TPL Summary
R1 requires to identify the individual and joint responsibilities of the Planning Coordinator (ERCOT) and Transmission Planners in ERCOT’s area for maintaining models and performing the study or studies needed to complete GMD Vulnerability Assessment.
R2 requires to maintain System models and GIC System (DC) models of the responsible entity’s planning area for performing the studies needed to complete GMD Vulnerability Assessment
Guidance for developing the GIC System model is provided in the GIC Application Guide developed by the NERC GMD Task Force and available at:
R3 requires to have criteria for acceptable System steady state voltage performance for its System during the benchmark GMD event described in Attachment 1.

6. TPL Summary
R4 requires a GMD Vulnerability Assessment of the system to determine its ability to withstand a Benchmark GMD Event without causing voltage collapse
Assessment performed once every five years
Applicability: Planning Coordinators, Transmission Planners
R5 requires to provide GIC flow information to be used for the transformer thermal impact assessment specified in R6 to each TO and GO that owns an applicable BES power transformer in the planning area.
Part 5.1 The maximum effective GIC value for the worst case geoelectric field orientation for the benchmark GMD event
Part 5.2 The effective GIC time series, GIC(t), calculated using the benchmark GMD event
Additional guidance is available in the Transformer Thermal Impact Assessment white paper: Disturbance-Mitigation.aspx

7. GMD Assessment Process Overview
Assemble model and equipment data
Create dc model of the system
Calculate GIC for each transformer
Calculate transformer reactive losses
Investigate mitigation options
Standard TPL Planning
GMD-specific Planning Steps
GIC calculation is now available on most power system analysis software
Identify voltage and system issues
Run ac power flow w/ reactive losses included
Conduct transformer thermal assessment

8. TPL Summary
R6 requires a Transformer Thermal Impact Assessment to ensure high-side, wye grounded BES transformers connected at 200kV or higher will not overheat based on the benchmark event
Applies to transformers where effective GIC identified in GIC studies 75 A per phase or greater (not 75 A continuous). Effective 75 A per phase is a conservative screening criterion
Approaches for conducting the assessment are presented in the Transformer Thermal Impact Assessment white paper posted on the project page
Performed once every five years with GMD Vulnerability Assessment
Applicability: Generator Owners, Transmission Owners

9. TPL Summary
R7 requires to develop a Corrective Action Plan addressing how the performance requirements will be met if through the GMD Vulnerability Assessment responsible entity determined that System does not meet the performance requirements of Table 1.
Assessment performed once every five years with GMD Vulnerability Assessment
Applicability: Planning Coordinators, Transmission Planners
Corrective Action Plans as defined in the NERC Glossary of Terms: A list of actions and an associated timetable for implementation to remedy a specific problem.

10. Benchmark GMD Event Description
The Benchmark GMD Event is described by:
Reference geoelectric field amplitude (8V/km)
1-in-100 year amplitude determined statistically from geomagnetic field measurements for a reference earth model
Used for GIC studies and load-flow simulations that account for transformer Reactive Power absorption caused by half-cycle saturation
Reference geomagnetic field waveshape
March 13-14, 1989 GMD event selected from recorded GMD events
Used for time-domain analysis on equipment such as transformer thermal impact assessment and/or to determine local geoelectric field if alternative or multiple earth models are used in GIC studies
Scaling factors for geomagnetic latitude and earth conductivity can be used to adjust geoelectric field amplitude

11. Epeak = Ebenchmark x α x β (in V/km)
Benchmark GMD Geoelectric Field
Epeak = Ebenchmark x α x β (in V/km)
Epeak = Benchmark geoelectric field magnitude at System location
Ebenchmark = 8 V/km Benchmark geoelectric field magnitude at reference location (60 N geomagnetic latitude, resistive ground model)
α = Factor adjustment for geomagnetic latitude
β = Factor adjustment for regional earth conductivity model
The benchmark GMD event description is available on the project page: hmark_GMD_Event_Dec5_clean.pdf

12. Questions and Answers